Prostate cancer is the most common malignancy in men with a lifetime incidence of 15.3% (Howlader 2012). Based upon data from 1999-2006 approximately 80% of prostate cancer patients present with early disease clinically confined to the prostate (Altekruse et al 2010) of which around 65% are cured by surgical resection or radiotherapy (Kattan et al 1999, Pound et al 1999). 35% will develop PSA recurrence of which approximately 35% will develop local or metastatic recurrence, which is non-curable. At present it is unclear which patients with early prostate cancer are likely to develop recurrence and may benefit from more intensive therapies. Current prognostic factors such as tumour grade as measured by Gleason score have prognostic value but a significant number of those considered lower grade (7 or less) still recur and a proportion of higher-grade tumours do not. Additionally there is significant heterogeneity in the prognosis of Gleason 7 tumours (Makarov et al 2002, Rasiah et al 2003). Furthermore it has become evident that the grading of Gleason score has changed leading to changes in the distribution of Gleason scores over time (Albertsen et al 2005, Smith et al 2002).
It is now clear that most solid tumours originating from the same anatomical site represent a number of distinct entities at a molecular level (Perou et al 2000). DNA microarray platforms allow the analysis of tens of thousands of transcripts simultaneously from archived paraffin embedded tissues and are ideally suited for the identification of molecular subgroups. This kind of approach has identified primary cancers with metastatic potential in solid tumours such as breast (van't Veer et al 2002) and colon cancer (Bertucci et al 2004).